Frost tolerant fins

ABSTRACT

A heat exchanger assembly for thermally conditioning a stream of air. The assembly includes a first and second manifolds extending in spaced and parallel relationship. A plurality of tubes extend transversly between the manifolds to establish fluid communication therebetween. A plurality of corrugated air fins is disposed between adjacent tubes with the cross-section of each air fin presenting a plurality of legs extending transversly between the flat sides of adjacent tubes. Each leg defines a plurality of front louvers including a leading half louver disposed adjacent the front edge of the leg and a plurality of leading louvers spaced from each other and from the leading half louver. A plurality of smaller trailing louvers are spaced from the leading louvers. A plurality of rear louvers being spaced from each other is disposed between the trailing louvers and the rear edge of each leg.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to heat exchangers and more particularly, to heatexchanger fins.

2. Description of the Prior Art

U.S. Patent Application No. 2007/0051502 to Shinobu Yamauchi andpublished on Mar. 8, 2007 (hereinafter referred to as Yamauchi '502)discloses a heat exchanger including a plurality of tubes extending inparallel and spaced relationship with each other and having a pluralityof air fins each presenting a plurality of legs extending transverselybetween the adjacent tubes to define a plurality of air channels for theflow of air between adjacent legs. Each leg has a front edge and definesa plurality of front louvers being spaced from each other and adjacentthe front edge to define a plurality of front air gaps. The frontlouvers present a plurality of leading louvers having a predeterminedleading louver width and a plurality of trailing louvers being spacedfrom the leading louvers. The leading width ranges from 0.8 to 1.3 mm.

Often heat exchangers, are used as outdoor evaporators in heat pumpsoperating in cold weather. In order to absorb heat from the outside airin such conditions, the coolant in the heat exchanger must operate atextremely low temperatures, often below the freezing temperatures ofwater. The cold and wet air causes moisture to condense on the leadingedge of the fins. The condensed moisture then may freeze and accumulateon the leading edge of the fins as frost. This frost obstructs the flowof air from passing through the air channels and between adjacentlouvers, which dramatically decreases the heat exchanger's performance.Since the frost accumulation is concentrated at the leading edges of thefins, the air channels can become blocked with a relatively small amountof frost. The heat exchanger must then be stopped and defrosted beforeit can resume operation.

SUMMARY OF THE INVENTION

The invention provides for such a heat exchanger assembly wherein theleading louver width ranges from 1.5 to 2.0 mm.

The larger leading louvers of the invention provide for increased spacefor the air to flow between adjacent louvers. The trailing louvers thenhave a smaller trailing louver width than the leading louver widthbecause they are not as susceptible to the frost accumulation of theleading louvers. The use of smaller trailing louvers minimizes theimpact of the reduction in heat transfer performance associated with thelarge leading louvers.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a perspective and exploded view of the heat exchangeraccording to the present invention;

FIG. 2 is a perspective and fragmentary view of the tubes, fins andlouvers according to the present invention;

FIG. 3 is a fragmentary view of one of the legs of the air fins andshowing the louvers;

FIG. 4 is a schematic view showing a cross-section of the louvers; and

FIG. 5 is a schematic view showing a cross-section of the louvers in anoperating condition with frost accumulation.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

Referring to the Figures wherein like numerals indicate correspondingparts throughout the several views, the invention includes a heatexchanger assembly 20 for thermally conditioning a stream of air. Theheat exchanger assembly 20 is generally shown in FIG. 1 and includes andfirst manifold 22 and a second manifold 24 being spaced and extending inparallel relationship with each other.

The first manifold 22 defines a plurality of first tube slots 26 spacedfrom each other, and the second manifold 24 defines a plurality ofsecond tube slots 28 being spaced to correspond with the first tubeslots 26 of the first manifold 22.

The heat exchanger assembly 20 further includes a plurality of tubes 30extending in parallel and spaced relationship with each other betweenfirst and second tube ends 32, 34. Each of the tubes 30 has across-section presenting flat sides interconnecting a round front 36 anda round back 38. In one embodiment, each tube 30 (generally indicated inFIG. 3) includes a tube divider 40 extending between the first andsecond tube ends 32, 34 to divide each tube 30 into first and secondpassages 42, 44. However, the tubes 30 may have any shape or features totransmit a fluid. For example, the tubes 30 could be hollow, they couldinclude a plurality of webs extending transversely between the flatsides of the tubes 30 to define a plurality of passages, or they coulddefine a plurality of microchannels extending between the first andsecond tube ends 32, 34.

The first tube end 32 of each tube 30 extends into one of the first tubeslots 26 of said first manifold 22 to establish fluid communicationbetween the first manifold 22 and the tubes 30, and the second tube end34 of each tube 30 extends into the corresponding second tube slot 28 ofthe second manifold 24 to establish fluid communication between thesecond manifold 24 and the tubes 30.

The assembly 20 further includes a plurality of air fins 46 disposedbetween and engaging the flat sides of adjacent tubes 30. Each of thefins 46 (generally indicated in FIG. 2 and generally shown in FIG. 3)includes a front edge 48 adjacent the round front 36 of the tubes 30 anda back edge adjacent the round back 38 of the tubes 30. Referring toFIG. 1, the cross-section of each of the air fins 46 presents aplurality of legs 50 extending transversely between the adjacent flatsides of the tubes 30. The legs 50 of the air fins 46 are interconnectedby bases 52 engaging the flat sides of alternating tubes 30 to present aserpentine pattern extending between the first and second manifolds 22,24. The serpentine pattern of the air fins 46 presents a plurality ofair channels for the flow of air between adjacent legs 50 of said airfins 46. While the air fins 46 of the exemplary embodiment have aserpentine pattern, the invention is meant to include any pattern fortransferring heat between the tubes 30 and the passing air.

Referring to FIG. 3, each of the legs 50 of the air fins 46 defines aplurality of front louvers 54 (generally indicated) and a plurality ofrear louvers 56 (generally indicated). The front louvers 54 are disposedadjacent the front edge 48 of each fin 46 and are spaced apart from eachother. The louvers 54, 56, 64, 66, 68 may be formed by any meansincluding but not limited to bending, cutting, soldering, welding,adhesion, etc.

Each of the front louvers 54 is disposed at a predetermined front louverangle Θ_(F) to define a plurality of front air gaps 58 in each of thelegs 50 of the air fins 46 for conveying air from a first air channel onone side of the leg 50 to a second air channel on the other side of theleg 50. The rear louvers 56 are disposed adjacent the rear edge 60 ofeach fin 46 and are spaced apart from each other. Each of the rearlouvers 56 is disposed at a predetermined rear louver angle Θ_(R) todefine a plurality of rear air gaps 62 in each of the legs 50 of the airfins 46 for conveying air from the second air channel to the first airchannel. The front and rear louver angles Θ_(F), Θ_(R) are preferably inthe range of 20 to 50 degrees and most preferably in the range of 35 to45 degrees. In the exemplary embodiment, the louver angle is depicted asconstant, but it is also possible to vary the louver angle to enhancethe effect achieved with variable louver width.

In the exemplary embodiment, a center rib 70 is disposed between thefront and rear louvers 54, 56 for turning the air flow and directing itto the rear louvers 56. Each center rib 70 has a center portion 72extending parallel to the leg 50 of the air fin 46 and includes a frontside 74 and a rear side 76 opposite from the front side 74. The frontside 74 extends transversely from the center portion 72 toward the frontlouvers 54 to define one of the front air gaps 58, and the rear side 76extends transversely from the center portion 72 toward the rear louvers56 to define one of the rear air gaps 62.

Referring to FIG. 4, the front louvers 54 include a leading half louver64 disposed adjacent the front edge 48 and a plurality of leadinglouvers 66 spaced from the leading half louver 64. Each of the leadinglouvers 66 has a predetermined leading louver width W_(l). The frontlouvers 54 also include a plurality of trailing louvers 68 disposedbetween the leading louvers 66 and the center rib 70, and each of thetrailing louvers 68 has a predetermined trailing louver width W_(t).

The rear louvers 56 define a trailing half louver disposed adjacent therear edge 60 of each fin 46. Each of the rear louvers 56 has apredetermined rear louver width W_(r).

The leading half louver width W_(lhl) is in the range of 0.75 to 1.50 mmand the leading louver width W_(l) is in the range of 1.5 to 2.0 mm. Thetrailing louver width W_(t) is less than the leading louver width W_(l)and is in the range of 0.9 to 1.5 mm, and consequently, each of thefront air gaps 58 is larger than each of the rear air gaps 62. In oneembodiment, the rear louver width W_(r) is less than the trailing louverwidth W_(t) of the front louvers 54. However, the rear louvers 56 mayalso be made to be a mirror image of the front louvers 54. Although itis not as efficient to have larger rear louvers 56 as having smallerrear louvers 56, it may decrease manufacturing costs to build an air fin46 that is symmetrical about its center rib 70 and is meant to beincluded in the scope of the invention.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A heat exchanger assembly for heating and/or cooling a stream of aircomprising: a plurality of tubes extending in parallel and spacedrelationship with each other; a plurality of air fins disposed betweenand engaging adjacent tubes and having a front edge and a back edge;said air fins defining a plurality of front louvers being spaced fromeach other and adjacent said front edge to define a plurality of frontair gaps; said front louvers including at least one leading louverhaving a predetermined leading louver width and at least one trailinglouver having a trailing louver width; said leading louver width beinggreater than said trailing louver width; and said leading louver widthranging from 1.3 to 2.5 mm.
 2. The assembly as set forth in claim 1wherein said leading louver width is further defined as ranging from 1.5to 2.0 mm.
 3. The assembly as set forth in claim 1 wherein said leadinglouver width is further defined as ranging from 1.9 to 2.0 mm.
 4. Theassembly as set forth in claim 1 wherein said trailing louvers have apredetermined trailing louver width ranging from 0.9 to 1.5 mm.
 5. Theassembly as set forth in claim 1 wherein said trailing louvers have apredetermined trailing louver width ranging from 1.00 to 1.25 mm.
 6. Theassembly as set forth in claim 5 wherein said trailing louver width isfurther defined as 1.14 mm.
 7. The assembly as set forth in claim 1wherein the cross-section of each of said air fins presents a pluralityof legs extending transversly between said adjacent tubes and defining aplurality of air channels for the flow of air between adjacent legs ofsaid air fins.
 8. The assembly as set forth in claim 7 wherein each ofsaid legs of said air fins includes a plurality of rear louvers beingspaced from each other and adjacent said rear edge to define a pluralityof rear air gaps in each of said legs of said air fin for conveying airfrom said second air channel to said first air channel.
 9. The assemblyas set forth in claim 8 wherein each of said legs of said air finsincludes a center rib disposed between said front louvers and said rearlouvers for directing airflow delivered from said first air channel tosaid second air channel by said front louvers back to said first airchannel.
 10. The assembly as set forth in claim 9 wherein said centerrib has a center portion extending parallel to said legs of said finsand has a front side extending transversely from said center portiontoward said front louvers to define one of said front air gaps adjacentto said front side and has a rear side opposite of said front side andextending transversely from said center portion toward said rear louversto define one of said rear air gaps adjacent to said rear side.
 11. Theassembly as set forth in claim 8 wherein said rear louvers have a rearlouver width ranging from 0.8 to 1.5 mm.
 12. The assembly as set forthin claim 8 wherein said rear louvers are disposed at a predeterminedrear louver angle ranging from 20 to 50 degrees.
 13. The assembly as setforth in claim 8 wherein said rear louvers are disposed at a rear louverangle ranging from 35 to 45 degrees.
 14. The assembly as set forth inclaim 1 wherein said front louvers are disposed at a front louver angleranging from 20 to 50 degrees.
 15. The assembly as set forth in claim 1wherein said front louvers are disposed at a front louver angle rangingfrom 35 to 45 degrees.
 16. The assembly as set forth in claim 1 furtherincluding a first manifold and a second manifold extending in spaced andparallel relationship with said first manifold; and each of said tubesextending between a first tube end engaging said first manifold and asecond tube end engaging said second manifold.
 17. The assembly as setforth in claim 16 wherein said first manifold defines a plurality offirst tube slots spaced from each other and engaging said tubes.
 18. Theassembly as set forth in claim 17 wherein said second manifold defines aplurality of second tube slots being spaced to correspond with saidfirst tube slots of said first manifold.
 19. The assembly as set forthin claim 18 wherein said first tube end of each of said tubes extendsinto one of said first tube slots of said first manifold to establishfluid communication between said first manifold and said tubes.
 20. Theassembly as set forth in claim 19 wherein said second tube end of eachof said tubes extends into said corresponding second tube slot of saidsecond manifold to establish fluid communication between said secondmanifold and said tubes.
 21. The assembly as set forth in claim 1wherein each of said tubes has a cross-section presenting flat sidesinterconnecting a round front and a round back.
 22. The assembly as setforth in claim 21 wherein each of said tubes includes at least one tubedivider dividing each tube into first and second passages and extendingbetween said first and second tube slots.
 23. The assembly as set forthin claim 21 wherein said legs of each of said fins are interconnected bybases engaging said flat sides of alternating tubes to present aserpentine pattern extending between said first and second manifolds.24. The assembly as set forth in claim 1 further including a leadinghalf louver disposed adjacent said front edge of each of said air fins.25. The assembly as set forth in claim 24 wherein said leading halflouver has a leading half louver width ranging from 0.75 to 1.50 mm. 26.A heat exchanger assembly for heating and/or cooling a stream of aircomprising: a first manifold presenting a plurality of first tube slotsspaced from each other; a second manifold extending in spaced anparallel relationship with said first manifold and defining a pluralityof second tube slots being spaced to correspond with said first tubeslots of said first manifold; a plurality of tubes extending in paralleland spaced relationship with each other between first and second tubeends; said first tube end of each tube extending into one of said firsttube slots of said first manifold to establish fluid communicationbetween said first manifold and said tubes; said second tube end of eachtube extending into said corresponding second tube slot of said secondmanifold to establish fluid communication between said second manifoldand said tubes; each of said tubes having a cross-section presentingflat sides interconnecting a round front and a round back; each of saidtubes including at least one tube divider dividing each tube into firstand second passages and extending between said first and second tubeslots; a plurality of air fins disposed between and engaging said flatsides of adjacent tubes and having a front edge adjacent said roundfront of said tubes and a back edge adjacent said round back of saidtubes; the cross-section of each of said air fins presenting a pluralityof legs extending transversely between said adjacent flat sides of saidtubes and interconnected by bases engaging said flat sides ofalternating tubes to present a serpentine pattern extending between saidfirst and second manifolds and defining a plurality of air channels forthe flow of air between adjacent legs of said air fins; each of saidlegs of said air fins defining a plurality of front louvers including aleading half louver and a plurality of rear louvers including a trailinghalf louver and a center rib disposed between said front and rearlouvers; said plurality of front louvers spaced from each other anddisposed at a predetermined front louver angle to define a plurality offront air gaps in each of said legs of said air fins for conveying airfrom a first air channel on one side of said leg to a second air channelon the other side of said leg; said plurality of rear louvers beingspaced from each other and disposed adjacent said rear edge of said airfin at a predetermined rear louver angle to define a plurality of rearair gaps in each of said legs of said air fin for conveying air fromsaid second air channel to said first air channel; said center rib beingdisposed between said front and rear louvers for directing airflowdelivered from said first air channel to said second air channel by saidfront louvers back to said first air channel; said center rib having acenter portion extending parallel to said legs of said fins and havingfront side extending transversely from said center portion toward saidfront louvers to define one of said front air gaps adjacent to saidfront side and having a rear side opposite from said front side andextending transversely from said center portion toward said rear louversto define one of said rear air gaps adjacent to said rear side; saidleading half louver being disposed adjacent said front edge of each legof said air fin and said trailing half louver being disposed adjacentsaid rear edge of each leg of said air fin; said front louvers includinga plurality of leading louvers spaced from said leading half louver andhaving a predetermined leading louver width; said front louversincluding a plurality of trailing louvers disposed between said leadinglouvers and said center rib and having a predetermined trailing louverwidth; said rear louvers having a rear louver width; said leading louverwidth of said leading louvers being wider than said trailing louverwidth of said trailing louvers; and said leading half louver widthranging from 0.75 to 1.50 mm; said leading louver width ranging from 1.3to 2.5 mm; said trailing louver width ranging from 1.00 to 1.25 mm; saidrear louver width ranging from 0.8 to 1.5 mm; and said front and rearlouver angles ranging from 35 to 45 degrees.